High frequency oscillation analysis and suppression strategy of flexible direct current system

Abstract

In recent years, the high frequency oscillation (HFO) accidents caused by long link delay in modular multilevel converter-based high-voltage direct current (MMC-HVDC) transmission projects have posed new challenges to the safety and stability of power system operation. This paper adopts delay stability margin to measure the high frequency stability of the MMC-HVDC system and derives the state space model of the MMC-HVDC time-delay system considering the link delay. The Lyapunov direct method is extended to the stability analysis of the MMC-HVDC time-delay system and the delay stability margin of the system is solved based on the linear matrix inequality (LMI). Then the influence of the controller parameters on the delay stability margin of the MMC-HVDC system is analyzed. Based on improved Smith predictive compensation control, an HFO suppression strategy of the MMC-HVDC system is proposed to improve the high frequency stability of the system by equivalently reducing and eliminating the total link delay. The effectiveness of the Lyapunov direct method for solving the delay stability margin of the MMC-HVDC system and the superiority of the proposed HFO suppression strategy are verified by the time-domain simulation in PSCAD/EMTDC. The research provides a novel viewpoint for the study of the HFO and suppression strategy of the MMC-HVDC system.